Also are there different medals for the different dates or just the one historian for any and all?

Sorry if I missed a post where it was covered earlier. It's a long thread and my A.D.D. kicked in.

For the historian achievement, you need to play just one on the right date (no matter which one, as long as it is one of the official scenarios), but there is also an advanced historian achievement, for which you have to play the 16 scenario's from the original rulebook on the right date.

Do you get different medals for the different games, or does one cover them all?

There is one award that you receive for playing any scenario on its anniversary (it doesn't matter which one). Advanced Historian is awarded if you play 15/16 of the base game scenarios on their anniversary. It's supposed to be 16/16, but there appears to be some kind of bug in it.